This invention relates to a punch tool grinding machine and method. Punch tools are typically made of hardened wear-resistant metal for use in impacting sheets of other material such as softer steels, aluminums, brass, or nonmetallic materials such as paper or cloth. The sheets of material are supported by a die having a hole therein corresponding in size and shape to the punch tool which is held in alignment therewith by a punch press or a stamping machine. The punch press or stamping machine applies high pressure or high impacting force to the punch tool to cause it to punch a hole in the material. It is important for the proper operation of the punch tool that the edges of the tool, which correspond to the shape of the hole desired, be maintained in a sharp condition.
As the punch tool is used repeatedly, the peripheral edges of the impacting face of the tool will wear, round-off, or otherwise deteriorate. Depending upon the material being punched, the resistance to shear may be very high. For example, twenty thousand to forty-five thousand pounds per square inch for aluminum (137.9 GN/m.sup.2 to 278.5 GN/m.sup.2) and thirty-five thousand pounds per square inch to one hundred fifty thousand pounds per square inch for steel (241.3 GN/m.sup.2 to 1,034 GN/m.sup.2). To withstand such pressures, the tools are necessarily made of hardened tool steel. Thus, grinding is required to sharpen the punch tools.
Punch tools come in various shapes and configurations, including flat shear faces, slanted or angled shear faces, roof-top or double shear face configurations, as well as hollow-ground shear faces. Efforts have been made to provide quick and efficient machines for grinding the faces of such tools. Previously these efforts have not been totally successful.
Alignment problems arise when tools to be ground have shear faces which are not perpendicular to the axis of the punch tool. Usually the shear face must be ground flat so that a sharp angle is formed along the intersection of the side and the face. Alignment by standard shimming and adjusting means is time consuming and costly, especially when the shear angles vary from tool to tool.
Attempts have been made to solve these problems using elaborate and expensive machines. For example, a tool grinder uses a special wheel designed for grinding on its side rather than on its circumference face. In this machine the punch tool face is aligned and held square to the side of the grinding wheel for grinding. When the face of the punch tool is perpendicular to the shank of the tool, alignment can be accomplished by grasping the shank in a chuck. However, in order to grind punch tools having a shear angle not perpendicular to the axis of the tool, it is necessary to prop up one side of the chuck at an angle using a dowel pin. The side of the rotating grinding wheel is then moved into grinding contact with the tool face. This method is cumbersome and it requires guesswork and tedious measurements to precisely place the dowel pin under the chuck to obtain the desired angle corresponding to the shear angle on the tool. Also, this requires a special grinding wheel designed for extensive side grinding.
Another machine for sharpening punch tools employs a wide sanding belt. To grind a punch tool which has an angular shear surface, a chuck and sine plate assembly are required. The entire chuck and sine plate assembly are rotated beneath the wide grinding belt. In order to sharpen a punch tool with a concave shear surface, a complex universal chuck is required. This complex chuck employs special cams and cam followers to manipulate the angle of the chuck and the punch tool held therein as the chuck is rotated beneath the grinding belt.
The present invention relates to an improved grinding machine which overcomes problems associated with existing punch tool grinding machines. An object of the present inventive machine is to permit quick alignment of a punch tool for grinding its face whether the tool face is perpendicular to its shank or whether the face is at a shear angle. Even multiple shear angle faces can be quickly aligned for grinding.
Another object of the present invention is to provide for use of a standard inexpensive grinding wheel which is designed for grinding at its periphery. A substantially constant grinding speed can be maintained because the high speed grinding surface at the periphery of the grinding wheel contacts the punch tool. Each abrasive particle at the periphery is at an equal distance from the axis of rotation and is traveling at the same speed. This compares favorably with grinding machines which rely upon a flat side to grind a flat surface. Where the side of the grinding wheel is used, the abrasive particles of the wheel which contact the punch tool near the center of the wheel have a slower relative speed than the abrasive particles of the wheel which contact the punch tool near the outside of the wheel.
Another object of the invention is to provide a grinding machine and method for grinding not only for various face configurations of punch tools, but also for grinding relief angles on the sides of punch tools.
Another object of the present invention is to provide an inexpensive grinding machine having an "x" axis along which a tool-holding rotating chuck can be moved and a "y" axis along which a motorized grinding wheel can be adjustably moved.
Another object of the invention is to provide a means for rotating the tool-holding chuck at a constant speed when desired and means for holding the chuck stationary at various indexed angles of rotation for performing a grinding procedure at such stationary position.
Another object of the present invention is to provide pivotable means for mounting the chuck on the "x" guideway so that is axis of rotation can be pivoted to desired angles from the "x" axis guideway on which it is mounted. A further object is to provide for index pins at predetermined chuck pivot angles.